LIFE ON EARTH may have originated from the RNA cousin of DNA, but how the modern world evolved from the RNA world remains largely unknown. Now, in a new study published last week in the journal NatureWhat researchers think are ancient remains from primordial molasses still lurking in modern biology may serve as the missing links bridging modern life to the RNA world.
THIS IS THE BACKGROUND – Today, the main building blocks of life are DNA, which can store genetic data, and proteins, including enzymes that catalyze important biological reactions. However, DNA requires protein to form, and protein needs DNA to form, raising the question of how protein and DNA could form without each other.
To help solve this mystery, scientists have suggested that life may at first depend largely on RNA. Compounds called nucleobases – adenine (A), thymine (T), cytosine (C) and guanine (G) – combine to form DNA. In RNA, uracil (U) is used as a substitute for thymine.
RNA can store genetic data like DNA, act as enzymes like proteins, and help make both DNA and proteins. The researchers speculated that DNA and proteins later replaced this RNA world because they were more efficient at their respective functions.
However, RNA molecules continue to play an important role in biology. For example, messenger RNA helps to carry genetic data from the DNA inside the cell nucleus to the rest of the cell. Transfer RNA mixed amino acids, the building blocks of proteins, to factories inside cells called ribosomes. Ribosomal RNA helps ribosomes synthesize proteins based on information from messenger RNA.
But how the chemistry of life moves beyond the RNA world is still not fully understood. Today, although RNA in ribosomes helps in the production of proteins, it cooperates with complex proteins to do so. It is not clear how the RNA world might have started protein synthesis before complex proteins existed to help produce proteins.
WHAT SCIENTISTS DO In the new study, the researchers examined molecules other than A, U, C, and G used in RNA. These so-called “non-standard RNA bases” are used in transfer and ribosomal RNA.
In RNA, bases are combined with sugar molecules to form compounds called nucleosides. Nucleosides can be combined with phosphorus-containing chemicals to create molecules called nucleotides. RNA is made up of chains of nucleotides.
The study’s senior author Thomas Carell, a biochemist at Ludwig Maximilians University in Munich, said non-canonical nucleosides – those that use different bases or sugars commonly found in RNA – today” necessary for the RNA to fold into a suitable three-dimensional structure”. Inverse. “They also give RNA the stability it needs to function.”
Furthermore, non-standard RNA nucleosides increase the accuracy of the system used to decode genetic information. “Without these nucleotides that decode the genetic information, the whole process is very error-prone,” Carell notes.
Non-canonical nucleosides can have amino acids bonded to them. Carell and his colleagues reasoned that such compounds may have provided a way for ancient RNA molecules to help with protein synthesis. They synthesized RNA strands incorporating such non-standard nucleosides to see what chemical reactions might take place.
WHAT THEY FIND – Scientists discovered that RNA strands possessing non-canonical nucleosides can form complex RNA chains and amino acid sequences called peptides. In modern biology, proteins are made of long peptides.
“For me, the most surprising discovery was how easily amino acids attach to RNA,” says Carell. “Peptides can magically grow on RNA essentially without much outside help.”
The researchers suggest that the RNA world consists of not only four canonical nucleosides, but many more. These non-canonical nucleosides helped the RNA world transition to the RNA-peptide world, a world of increasingly longer and more complex molecules that gave rise to the DNA-RNA-protein world. Finally, four canonical nucleosides have evolved to help encode data, while other non-canonical nucleosides help provide structure and stability.
“One potential criticism might be that this type of RNA-peptide conjugate we are proposing is no longer found in nature today,” says Carell. However, the scientists believe that “the fact that amino acid-containing nucleosides persist in the transport RNA is sufficient evidence that such structures may indeed exist.”
WHAT NEXT? In the future, scientists want to find peptides grown on RNA that can act as an enzyme that life needs to function properly. “Particularly important is the discovery of peptides that can help RNA replicate or provide more stability to the RNA molecule,” Carell said.
https://www.inverse.com/science/origin-of-life-primordial-world-mystery-rna-dna Scientists may have found a missing link between the primordial world and modern life